Presentation on theme: "Three Domains of Life Protists. Three Domains of Life."— Presentation transcript:
Three Domains of Life Protists
Three Domains of Life
Changes in Classification The ‘old school’ method of classification included 5 Kingdoms (what I learned in school) –Monera –Protista –Fungi –Plantae –Animalia Today, advances in molecular technology expanded our understanding (and interpretation) of systematics
Modern Systematics Three Domain classification of life Numerous, virtually countless Kingdoms Bacteria and Archaea are now 2 distinct Domains (once included together in Kingdom Monera) Protista, Fungi, Plantae, and Animalia remain classified as distinct Kingdoms, although classification of the kingdom Protista has been met with complications
Prokaryotes Includes the kingdoms Archaea & Bacteria Oldest, structurally-simplest, and most abundant forms of life Photosynthesis Bacterial and Eukaryotic Diversity Important decomposers and symbionts
Prokaryotes Unicellular Typically 1μm or less (1000 μm = 1mm; 1000mm = 1 meter) No membrane-bound nucleus; instead a single circular chromosome made of DNA Asexual reproduction by binary fission Photosynthetic bacteria utilize oxygen or chemical compounds, such as sulfur
Prokaryotic Cell Structure Three basic forms: –Bacillus – rod-shaped –Coccus - sphercal or ovoid-shaped –Spirillum – spiral or helical
Prokaryotic Cell Structure Prokaryotes have a tough cell wall and other external structures Cell wall consists of peptidoglycan; a rigid network of polysaccharide strands cross-linked by peptide side chains; unique to Bacteria Maintains the shape of the cell and protects it from swelling and rupturing
Prokaryotes can have 1 or more flagella (much less complex than in Eukaryotes) Some Prokaryotes possess pilli, which helps fasten cell to host membrane
Domain Archaea Once considered a subdivision of the Kingdom Monera, now its own domain Like all prokaryotes, Archaea are single- celled microorganisms that lack a nucleus and membrane-bound organelles Best known for the “extremophiles” – Archaea which thrive in extremely harsh environments
Archea - Extremophiles Thermophiles – thrive at 60-80°C (>176°F!) Acidophiles – thrive at pH at or below pH 3 Xerophiles – grow in extremely dry conditions Halophiles – require extremely high concentrations of salt
Archaea - Extremophiles Evidence for evolution of life on Earth? Many of the harsh conditions which extremophiles require to survive were characteristic of our early Earth Likely that extremophiles evolved to dwell in such conditions billions of years ago and retained ability to survive today in specific environments
Archaea differ from Bacteria in numerous ways –Plasma membranes are made of different kinds of lipids –RNA and ribosomal proteins more like those of Eukaryotes –Mostly anaerobic Photosynthetic
Domain Bacteria Two types: –Gram-positive –Gram negative Refers to the Gram Stain (purple dye) Gram-positive bacteria – possess a thicker peptidoglycan cell wall; retain stain Gram-negative bacteria – contain less peptidoglycan; do not retain stain
Gram-positive and negative
Bacterial Conjugation Transfer of genetic material Horizontal gene transfer NOT sexually (no gametes)
Eukaryotic origin The nucleus and endoplasmic reticulum arose from infolding of the prokaryotic cell membrane
Eukaryotic origin Eukaryotic organelles arose from a consortium of symbiotic prokaryotes –Mitochondria were aerobic heterotrophic prokaryotes –Chloroplasts (for photosynthesis) were photosynthetic prokaryotes
Endosymbiotic theory Evidence? –Mitochondria have their own independent DNA, and a double membrane –Chloroplasts resemble cyanobacteria; also have their own independent DNA and a double membrane
Kingdom Protista (the trouble-maker) Kingdom Protista is NOT monophyletic Paraphyletic – includes common ancestor but not all descendents
Kingdom Protista Eukaryotic (must be! Domain Eukarya) Largely unicellular with some multi-cellular ‘exceptions’ (e.g., kelps, seaweed) May be autotrophic or heterotrophic Debate over classification – –Are some protists members of other kingdoms? –Would protists best be considered as several different kingdoms?
Kingdom Protista Characterized by: –Mode of locomotion (e.g., flagella, cilia) –Mode of nutrition (e.g., autotrophic, heterotrophic) –Body form (unicellular, multicellular) –Pigmentation (e.g., Red, Green, Brown alga) –Reproduction (asexual, sexual) Multicellular protists are distinguished from other Kingdoms by their lack of specialized tissues
Have you ever eaten a protist?, or should I ask, have you ever eaten seaweed??? Just to complicate matters, green algae is categorized as a plant in Kingdom Plantae…
Green Plants evolved from Green Algae We’ll come back to this…
Unicellular and multi-cellular ~1.5 million species Important decomposers Includes many disease-causing organisms Others are important symbionts and fermenting organisms
Kingdom Fungi Mycology – the study of fungi All fungi are heterotrophic –Obtain their food by secreting digestive enzymes and absorbing the nutrients released by the enzymes Unicellular fungi may have flagella; multicellular fungi are primarily filamentous in form Cell walls composed of chitin
Kingdom Fungi Phylogeny based on the 5 major Phyla (based on mode of sexual reproduction)
Kingdom Fungi Multicellular fungi consist of long, slender filaments called hyphae Some hyphae are continuous; others are divided by septa Mycelium – a mass of connected hyphae
Kingdom Fungi Mycelium grows through and digests its substrate Fungi live in their food!
Kingdom Fungi Hyphae (mycelium) form complex structures A mushroom is a spore-bearing body of a fungus; composed of hyphae A puffball is a spore-bearing body of certain species of fungi, including the deadly Death Cap mushroom; composed of hyphae
Kingdom Fungi Fungi can also be monokaryotic or dikaryotic –Monokaryotic – one nucleus per cell –Dikaryotic – two nucleii per cell Fungi reproduce sexually and asexually –During sexual reproduction in some fungi, 2 haploid nuclei fuse creating a dikaryotic (dikaryon) stage, which precedes the normal diploid nucleus
Kingdom Fungi Some fungi produce specialized mycelial structures to house spores (e.g., mushroom, puffballs, ‘shelf’ mcycelium on dead trees) Spores can form as a result of sexual or asexual reproduction Spores can withstand degradation and survive for long periods of time; because of their size, they can travel long distances
Kingdom Fungi Chestnut Blight – a fungal disease which has virtually eliminated the American chestnut Accidentally introduced into the U.S. on imported lumber from Asia The roots of the tree are fairly resistant to the fungus, but the tree succumbs once it grows enough shoots to reproduce Unknown spreading agent (the spores are everywhere!)
…Jack Frost nippin’ at your nose… The American chestnut once covered large tracts of forest in the U.S. The chestnut was a very important source of food for wildlife (and the inspiration for at least 1 Christmas song…) At the turn of the twentieth century, one quarter of all trees in the eastern United States were chestnut!
The Chestnut Blight Only a few mature survivors remain of the American Chestnut, which once consisted of 4 billion trees (that’s over 99.99% gone) If you have ever eaten a chestnut, you had a European import; only our grandparents may have ever tasted an American chestnut The American Chestnut Foundation seeks to restore the great chestnut, but how?
The Chestnut Blight Development of blight-resistant American chestnuts is accomplished through a process known as “backcross breeding” Hybrids between American and Chinese chestnuts are repeatedly crossed back onto purely American specimens, yielding offspring which are blight- resistant The resulting offspring are ~94% American (6% Chinese) and disease-resistant
Kingdom Fungi Spores are frequently dispersed by wind, but may also be spread by insects and small animals Chytrids are an ancestral group and retain flagella; have motile zoospores
Why did the mushroom go to the party? Many fungi live underground, and can reach great sizes One of the largest living organisms in the world is a fungus! The largest known specimen covers more than 3.4 square miles and is thousands of years old And some species of fungi are bioluminescent!
Armillaria fungus Connected underground by hyphae!
Fungal Ecology Fungi often have interactions or symbioses with other organisms Obligate symbiosis – essential for survival; fungus cannot survive without symbiont Facultative symbiosis – fungus can survive without symbiont Mutualistic relationships – both partners benefit Commensal relationships – one partner benefits, but the other is unaffected
Fungal Ecology A lichen is a symbiotic association between a fungus and a photosynthetic partner (usually green algae or cyanobacteria)
Fungal Ecology Mycorrhizae – association between a fungus and the root of a tree Mycorrhizae function as an extension of the plant root system; the fungus increases surface area for absorption and aids in transfer of nutrients The plant, in return, supplies organic carbon to the fungus
Mycorrhizae Very important! Mycorrhizal plants are more resistant to drought and even microbrial soil-borne pathogens Two types –Arbuscular mycorrhizae –Ectomycorrhizae
Fungal Ecology Leaf-cutter ants – an animal symbiont with fungi! The ants feed on special structures produced by a fungus that they have domesticated The ants feed the fungus leaves and protect it from pests and molds In return, the ants eat the fungus and feed it to their young